The dehydroiodination of 1-iodobutane has been investigated over two different nanocrystalline MgO samples. The reaction with clean MgO takes place at temperatures as low as 100 degreesC. However, a temperature of 300 degreesC or higher is required for catalytic dehydroiodination to take place. At lower temperatures the reaction stops after the maximum degree of surface modification with iodine is reached. It was found by XPS that at all temperatures iodination is limited to the surface and no bulk MgI2 is formed. The weight gain never exceeds 22%, which corresponds to 3.7% MgO conversion. In accordance with this conclusion, the textures of the samples after reaction are similar to those of the initial MgO. The surface iodination leads to a change in reaction mechanism: from concerted E2 elimination on initial MgO to stage E1 elimination. The secondary process of 2-iodobutane formation over iodinated samples was also established. (C) 2004 Elsevier Inc. All rights reserved.